The peppered moth occurs in two forms, i.e. light coloured (Biston betularia typoica) and dark coloured (Bistort betularia carbonaria).
Before industrial revolution Only light coloured moths were prevalent. Light coloured moths camouflaged well with the lichens that covers tree trunks, on the contrary dark moths were easy prey on the tree trunks and were very rare.
During the industrial revolution The population of dark coloured moth increased. While, that of light coloured moth decreased. This change was due to the burning of coal in factories.
The smoke from the factories killed the lichens and the tree trunks turned black due to the deposition of soot. The black moths had an advantage against soot, therefore, escaped predation of birds while on the other hand, white moths were identified in sharp contrast and become easy prey.
"With the progression of industrial revolution The coal was replaced by oil and electricity.
This resulted in reduction of soot deposits on the tree trunk. Gradually, the population of black moth decreased and that of light math began to increase.